1. Field of the Invention
The present invention relates to an autofocus (AF) adjustment device and a method thereof, and more particularly, to an autofocus control technology suitable for an electronic camera provided with an image pickup element.
2. Description of the Related Art
Conventionally, an electronic camera system is proposed which uses both the following AF systems: an AF of contrast system (contrast AF) that uses a high frequency component of an image signal obtained from an image pickup element such as a CCD; and an AF of active system (external light AF) that projects light onto an object from a phototransmitter and receives the reflection of light with a photoreceptor and measures a distance from the object using the principles of triangulation (Japanese Patent Application Publication Nos. 5-210042, 5-210043, 2001-141982, 2001-141983, etc.). These conventionally proposed systems are designed to select a focusing system from measurement results of the external light AF sensor, for example, by adopting the contrast AF when the distance from the object is small (Japanese Patent Application Publication No. 5-210043) or performing the external light AF for low brightness (Japanese Patent Application Publication No. 2001-141983).
Furthermore, another system is also proposed which moves the lens close to the focus position according to the result of the external light AF and then carries out the contrast AF (Japanese Patent Application Publication Nos. 8-184890 and 2001-141984).
However, Japanese Patent Application Publication Nos. 8-184890 and 2001-141984 neither refer to a search range of the contrast AF after the lens is moved close to the focus position according to the external light AF nor assume further autofocusing according to the result of the contrast AF. Moreover, these publications do not describe areas subject to the contrast AF.
In the case of a system that uses both the contrast AF and the external light AF, it is assumed that distance measurement results of the external light AF may vary due to influences of the object. Furthermore, distance-measuring points by the external light AF sensor may deviate from the center (AF target mark) of the angle of view of the image captured due to a parallax between the external light AF sensor and image pickup lens.